In the paper industry, in particular for the production of toilet rolls, kitchen paper or similar, large reels (parent reels) of tissue paper coming directly from the continuous production machine are wound. These large reels are then unwound and rewound to produce rolls or logs of smaller diameter, corresponding to the diameter of the finished product intended for sale. These rolls have an axial length equal to a multiple of the finished roll intended for distribution and sale and are therefore cut by cutting-off machines to obtain the finished product for packaging and subsequent sale. For the production of logs or rolls of web material, the modern rewinding machines are provided with winding rollers which, combined and arranged in various ways, and appropriately controlled, allow automatic production in rapid sequence of logs or rolls by continuous feed of the web material. After a roll has been wound, it must be moved away from the winding area, severing (by cutting, tearing or other method) the web material so that the next roll or log can be wound. Normally winding is performed around winding cores, typically but not exclusively made of cardboard, plastic or other similar suitable material. In some cases winding is performed around extractable recyclable spindles, which are removed from the finished roll and reinserted in the rewinding machine in order to wind the next roll.
In more modern rewinding machines, the winding movement is imparted to the logs or rolls being formed by the contact of two or more rollers rotating at controlled speed. These rewinding machines are called peripheral or surface rewinding machines, since the winding movement is imparted peripherally by contact between the surface of the winding rollers and the surface of the rolls or logs being formed. Examples of automatic continuous surface rewinding machines of this type are described in U.S. Pat. No. 5,979,818 and in other patents of the same family, and in the patent literature cited in this patent.
These machines are also called continuous and automatic, as the various phases of the winding cycle of each roll follow one another automatically, passing from the production of one roll to the next, without interrupting the feed of the web material and at roughly constant or substantially constant speed.
In some known embodiments the peripheral rewinding machines are also provided with central winding control systems in order to obtain higher quality products. The central control is obtained by means of a spindle or a pair of motorized tailstocks engaged with the winding core. Examples of machines of this type are described in U.S. Pat. No. 7,775,476 and in the publication US-A-2007/0176039, the content of which is incorporated in the present description and which can be referred to for further details relative to these types of devices.
In these machines the core around which the roll forms is kept in rotation and controlled in its movement by the combined effect of peripheral winding rollers and motorized tailstocks which engage the ends of the winding core for at least a part of the formation cycle of each roll or log.
One of the critical phases in the automatic continuous peripheral rewinding machines of the type described above is the so-called exchange phase, i.e. severing of the web material, unloading of the completed roll and beginning of winding of a new roll around a new winding core inserted in the winding nip.
Various solutions have been studied to perform these operations automatically, rapidly and effectively, for example via the use of winder rollers rotating at a controlled speed which accelerate and/or decelerate in a synchronized manner in order to favor correct movement of the completed rolls and new cores. In some cases tear systems are provided, where the web material is separated after winding by means of speed difference. In other cases pressurized air or suction systems, mechanical systems or similar are used to sever the web material.
Control of the winding rollers and means for separation or severing of the web material is one of the critical aspects of the exchange phase of the finished roll and its replacement with the new winding core for the formation of the next roll.